The invention relates generally to the field of bonded polymeric fiber structures and, more particularly, to multi-layer structures having nanofibers embedded in and around the interfaces between layers of bonded microfiber sub-structures. Such structures form very efficient filters for a variety of liquid and gas filtration applications.
In the science of filtration, the achievement of high filtration efficiency and concomitant low pressure drop (or flow resistance) has been quite difficult. In order for a filter to be engineered to provide excellent filtration efficiency of fine particles, either in liquid or gas filtration applications, the pore size of the filtration media must be small in relation to the size of the particles being excluded by the filter. However, conventional filter media, be it fibrous or made of particulate matter (e.g. sintered plastic or metal beads) is typically comprised of components that are of a size either larger than, or on the order of, the particulates being filtered. In such media, one reduces pore size to improve efficiency by increasing filter media thickness. When such filter media are employed, however, the pressure required to force the fluid (either liquid or gas) through the pores of the filter can become quite large, thus limiting the utility of the filter. The use of thicker and heavier media to improve efficiency also has the related disadvantage of low recovery of desired ingredients caught within the filter media, which causes filter media fouling.
One solution has been to form high performance, low pressure drop filters from sintered metal wire, where the metal fibers, typically of stainless steel composition, are constructed in either a woven or non-woven structure. These filters are widely used as final, fine filtration elements in ink jet printing applications, and are generally disposed adjacent the print head. They are used to prevent particles of too large size from fouling the print head, which would lead to clogging and misfires. The metal structure provides an additional benefit in that it is very abrasion resistant, and can withstand rubbing, frictional and other forces most commonly found in ink jet printers when the user installs, removes or changes the ink jet cartridge.
These woven or non-woven stainless steel fine ink filters are typically supplied in sheet or roll form, and are die cut into the desired shape for installation into either the ink jet cartridge or, in the case of printers which have the print head installed in the printer rather than the cartridge, installed in the ink conduit just prior to the print head. In both cases, the manufacturer of either the cartridge or the printer itself must die cut this hard, stainless steel, install it into a housing that is most typically made from a plastic such as polypropylene, and then affix it to the housing in such a manner so that it will be permanently attached and not subject to leakage or loosening. To do this, complex manufacturing methodologies may be employed to form a bond between the metal filter and the plastic housing. There are deficiencies in this manufacturing methodology in that the forces required to die cut the stainless steel filter may be large and the filter installation technologies may be complex and expensive.
There is accordingly a need for a fine filter for ink jet printer fine filtration applications, which has excellent fine particle filtration capability, low pressure drop, excellent abrasion resistance, is readily die cuttable, and is ultrasonically (or otherwise thermally) bondable to the plastic components typically found in ink jet printer construction.